1. Field of the Invention
The invention relates to low-power power supplies, and more particularly to low-power power supplies capturing power from a telephone line.
2. Description of the Related Art
Mobile computers, particularly laptop computers and notebook computers, have become increasingly popular. They have performance and capabilities near that of a desktop unit, and if color active matrix liquid crystal displays are utilized, the display is as good as a desktop unit. When combined with the mobility, the popularity is quite understandable. However, one problem with using portable computers is that often they need to be connected to various equipment. For example, when located in a office, it is desirable to connect to various office wide items or non-portable items. For example, a network interface is often necessary, as is a SCSI port for use with various external devices such as CD-ROMs. This situation has conventionally been handled using expansion bases, which contain expansion cards for network and SCSI use and connections for a video monitor, a printer and a full size keyboard, or port replicator strips, which are used to simply provide the connections to the monitor, printer and keyboard without the need for expansion cards.
One of the computer applications which is becoming prevalent is electronic mail or E-mail. The modern business often has a local area network (LAN), with E-mail and appointment calendar applications. A remote user, such as the laptop user away from the office needs to check periodically to maintain in full contact. Thus, a very common addition to a portable computer is a modem to allow remote access to the LAN or other dial up services. Typically this modem is installed in the laptop computer, not directly in any expansion base. So while an expansion base or port replicator may alleviate certain wiring problems, as the various cables need not be disconnected or connected when removing or installing the portable computer, it does not resolve the wiring concerns in the case of a modem, where a separate telephone line is still required to be plugged and unplugged into the modem in the computer. This results in aggravation for the user. Further, this telephone line is yet another of the tangled mass of cables utilized with the modern computer. While the monitor, keyboard and SCSI cables are generally located right next to the computer to interconnect the various components, the telephone line often has to be strung across an office and thus is either unsightly or very difficult to route. This is a further drawback to standard conventional modem communications where the modem is contained in the personal computer, be it a laptop or a desktop unit.
Thus the use of a modem in a laptop computer results in aggravations for the user and additionally requires unsightly and cumbersome cabling. Therefore it is clearly desirable to simplify both the laptop portability concerns and the unsightly wiring problem. One solution to this problem is a cordless modem system where a mobile station unit (MSU) is located in the computer or connected to the computer and a base station unit (BSU) which is connected to the telephone line. A radio frequency (RF) link is developed between the two units to allow a cordless connection between the computer and the telephone line. Such a system is further disclosed in Ser. No. 08/242,122, filed concurrently herewith and now abandoned, entitled "Cordless Modem System Having Multiple Base and Remote Stations which are Interusable and Secure," and in Ser. No. 08/242,302, also filed concurrently herewith, entitled "Cordless Modem System Having Base and Remote Stations which is Communications Software Transparent." Both of these applications are incorporated by reference and have been commonly assigned to the assignee of the present application.
Yet another extraneous cable would conventionally be present in such systems, however. The BSU would typically be powered by connection to a wall outlet, thus requiring both the connection to that outlet as well as connection to the telephone line. It would be greatly desirable if such a BSU, and other telephone line interface equipment, did not require connection to a wall outlet for power, thereby reducing the number of cables and greatly simplifying installation of the BSU.